The present invention relates to a process for producing propylene homopolymers or propylene-xcex1-olefin random copolymers using a highly active and highly stereoregular catalyst component.
In producing propylene homopolymers or propylene-xcex1-olefin random copolymers, high activity catalysts have industrially very high utility value because the residual catalyst is not necessary to remove from the polymer produced by polymerization, which allows simple after-treatment process of the polymer.
A gas-phase polymerization method is one of the processes of production effectively utilizing the characteristic of high activity catalysts. In applying the high activity catalysts to the gas-phase polymerization, however, lump and string-like irregular shape polymer is formed when the heat of polymerization is removed insufficiently. As a remedy to prevent the formation of lump and string-like irregular shape polymer, Japanese Examined Patent Publication No. (hereinafter referred to as JP-B 52-45749/1977, JP-B 60-26407/1985, JP-B 61-9964/1986, JP-B 64-10532/1989, National Stage of International Application No. (PCT JP-A) 61-502061/1986, and Japanese Unexamined Patent Publication No. (hereinafter referred to as JP-A 5-117317/1993 disclose processes for polymerization of olefins using said catalysts after preliminary polymerization of ethylene and/or xcex1-olefin. JP-A 50-119885/1975 discloses a method for eliminating particle-size distribution and preventing irregular growth of particles and aggregation of a large number of small particles which form a polymer lump, by altering the quantity of transient metal component in the supported catalyst. Further, JP-A 54-139986/1979 discloses a method for eliminating of blockage in a catalyst-supplying tube to prevent formation of a polymer lump by supplying a suspension of preliminary polymerized catalyst from the inner tube of a double tube nozzle and liquefied propylene from the outer tube. Moreover, JP-A 9-278807/1997 discloses a method for preventing formation of a polymer lump by irradiating xcex2-ray to the inside of the polymerization vessel. These methods, however, necessitate using an expensive apparatus of no practical use, or are insufficient in preventing formation of irregular shape polymer such as lump. The lump is formed in large quantity in a range of high comonomer concentration, and there is no sufficient remedy for preventing formation of polymer lumps.
The present inventors, in producing propylene homopolymers or propylene-xcex1-olefin random copolymers using a high activity catalysts, worked assiduously to elucidate an alternative process in which formation of the polymer lumps is least. As a result, we found that polymers with the least amount of polymer lump could be obtained by carrying out the polymerization reaction with addition of an organosilicon compound after pre-activation treatment of a supported Ziegler-type catalyst. The present invention was completed based on this finding.
The object of the invention is to provide the above-mentioned process for producing propylene homopolymers or propylene-xcex1-olefin random copolymers using a supported Ziegler-type catalyst, wherein formation of irregular shape polymer such as polymer lump decreases and a long-term and stable operation is allowed.
The invention is composed of the following items (1)-(2).
(1) A process for producing propylene homopolymers or propylene-xcex1-olefin random copolymers which comprises:
in a process for producing propylene homopolymers or propylene-xcex1-olefin random copolymers using a stereoregular catalyst which comprises a titanium-containing solid catalyst component (A) an organoaluminum compound (B) of the general formula AlR1 mX3xe2x88x92m (wherein R1 is a hydrocarbon group of 1-20 carbon; X is a halogen; m is an integer of 3xe2x89xa7m greater than 5), and if required an organosilicon compound (C) of the general formula R2xR3ySi(OR4)z (wherein R2 and R4 each is a hydrocarbon group; R3 is a hydrocarbon group or a hydrocarbon group containing a heteroatom or atoms; 0xe2x89xa6Xxe2x89xa62, 1xe2x89xa6Yxe2x89xa63, 1xe2x89xa6Zxe2x89xa63, and X+Y+Z=4),
[I] before carrying out homopolymerization of propylene or copolymerization of propylene with an xcex1-olefin other than propylene, using the titanium-containing solid catalyst component (A), an organoaluminum compound (Bxe2x80x2) of the general formula AlR5mX3xe2x88x92m (wherein R5 is a hydrocarbon group of 1-20 carbon atoms; X is a halogen atom; m is an integer of 3xe2x89xa7m greater than 1.5), and if required an organosilicon compound (Cxe2x80x2) of the general formula R6xR7ySi (OR8)z (wherein R6 and R7 each is a hydrocarbon group; R8 is a hydrocarbon group or a hydrocarbon group containing a heteroatom or atoms; 0xe2x89xa6Xxe2x89xa62, 1xe2x89xa6Yxe2x89xa63, 1xe2x89xa6Zxe2x89xa63, and X+Y+Z=4),
[II] treating the titanium-containing solid catalyst component (A) for pre-activation with propylene or ethylene and/or xcex1-olefin of 4-20 carbon atoms, and
[III] using the catalyst which is prepared by adding an organosilicon compound (Cxe2x80x3) to the pre-activated stereoregular catalyst in a molar ratio of 0.1-50 as Si/Ti.
(2) A process as described in the above item 1, wherein the process for producing propylene homopolymers or propylene-xcex1-olefin random copolymers is of a gas-phase polymerization.